Vestibular stimulation system and method

ABSTRACT

An apparatus and method in which the portions of the labyrinth associated with the labyrinthine sense and/or the nerves associated therewith are stimulated to perform at least one of the following functions: augment or control a patient&#39;s respiratory function, open the patient&#39;s airway, induce sleep, and/or counteract vertigo. In one embodiment, the vestibular stimulating system of the present invention includes 1) a stimulation element that performs the actual stimulation of the tissue, 2) a sensor to detect a physiological condition of the patient, and 3) a power/control unit that receives the signals provided by the sensor and causes stimulation energy to be provided to the stimulation element at an appropriate timing, level, pattern, and/or frequency to achieve the desired function. However, the present invention also contemplates eliminating the sensor in favor of applying a predetermined pattern of stimulation to the patient.

CROSS-REFERENC TO RELATED APPLICATIONS

This application is a Continuation-In-Part and claims priority under 35U.S.C. § 120 from U.S. patent application Ser. No. 09/563,552 filed May3, 2000, now U.S. Pat. No. 6,314,324, which claims priority under 35U.S.C. § 119(e) from U.S. provisional patent application No. 60/132,627filed May 5, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an apparatus and method of stimulatingthe vestibular system of a patient to provide a therapeutic benefit,and, in particular, to an apparatus and method in which the portions ofthe labyrinth associated with the labyrinthine sense and/or the nervesassociated therewith are stimulated to perform at least one of thefollowing functions: augment or control a patient's respiratoryfunction, open the patient's airway, induce or promote sleep, counteractvertigo, or a combination of these functions.

2. Description of the Related Art

There are numerous techniques for providing respiratory assistance to apatient suffering from a respiratory disorder and/or dysfunction. Forexample, it is known to provide mechanical ventilatory assistance bydelivering a flow of breathing gas to the patient's airway via aventilator. This mechanical ventilation method of assisting thepatient's respiratory effort has numerous disadvantages that are welldocumented. For example, the patient interface device, such as atracheal tube, intubation tube and nasal/oral mask, can be difficult toplace within or on the patient, may cause long-term problems in thepatient, and/or may not be tolerated by the patient. In addition,because the mechanical ventilator replaces, either partially orcompletely, the respiratory effort of the patient, the patient may havedifficulty being weaned off of the ventilator, especially if the patienthas been using a ventilator for an extended period of time.

It is also known to provide ventilatory assistance to a patient bydirectly stimulating the patient's phrenic nerve, thereby causing thediaphragm to contract. It is also known to provide this so called“electroventilation” technique by placing electrodes on the chest of thepatient to innervate the diaphragm or chest muscles directly. See, e.g.,U.S. Pat. No. 4,827,935 to Geddes et al. entitled, “DemandElectroventilator.” However, these conventional electroventilationtechniques are relatively ineffective at imitating the naturalrespiratory function of the patient, because, in a normal patient, eachrespiratory effort involves a complex interaction of nerve and musclestimulation that includes more tissues than just the phrenic nerve anddiaphragm. Conventional electroventilation techniques target individualmuscles or, at best, muscle groups, not the overall neural-muscularsystems that cooperate to produce a normal respiratory cycle.

There are also numerous techniques for maintaining airway patency and/orpatient ventilation to treat sleep apnea syndrome. For example, a commontechnique for treating obstructive sleep apnea (OSA) is to provide thepatient with a continuous positive airway pressure (CPAP) or a bi-levelpressure that varies depending on whether the patient is in theinspiratory or expiratory phase of the respiratory cycle. The supply ofgas to the patient provides a pneumatic splint for the portion of theairway that would otherwise collapse. It is also known to treat centralsleep apnea (CSA) using a system similar to a non-invasive ventilator.Preferably, the CSA treatment system detects whether the patient hasstopped breathing for a period of time that exceeds a predeterminedthreshold time period and provides ventilatory assistance if thisoccurs. These techniques for treating sleep apnea syndrome havedisadvantages similar to those associated with providing ventilatoryassistance to the patient; namely, some patients have difficultytolerating the patient interface device. In addition, some patients havedifficulty and/or are uncomfortable breathing against the flow of gasbeing delivered to their airway. Also, because these systems are usedwhile the patient sleeps, they must be kept as quite as possible so asnot to arouse the user or the user's sleep partner.

It is also known to treat OSA by electrically stimulating themusculature in the neck area associated with the upper airway.Relaxation of these muscles during sleep is believed to be acontributing, if not a primary, factor on the occurrence of OSA for manysufferers. One conventional method of electrically stimulating themuscles in the upper airway involves placing an electrode in directcontact with a surface of the patient and passing a current through thesurface tissues to stimulate the underlying muscles. For example, anintraoral appliance has been developed that applies an electricalcurrent within the oral cavity to induce contraction of the genioglossusmuscle, thereby helping to maintain airway patency. Another knownelectrical stimulation appliance applies electrical energy to theexterior surface of the patient's neck below the chin to inducecontraction of the underlying upper airway muscles.

Electromuscular stimulation using surface mounted electrodes createsrelatively large current densities at the site of the electrodes.Because these current densities are disposed at the surface of thepatient, which also typically contains a relatively large number ofnerve endings, such electrical stimulation devices might, in some cases,cause unpleasant sensations, possibly arousing the user from sleep. Inaddition, some patients may not be comfortable wearing an electricalstimulation appliance either on their neck or in their mouth while theysleep.

It is also known to apply electrical stimulation directly to the nervesand/or muscles of the upper airway via electrodes implanted in thepatient to induce tension in the muscles of the upper airway, therebypreventing them from collapsing during sleep. As with stimulating thephrenic nerve to induce respiration, these conventional neural-muscularelectrical stimulation techniques are relatively ineffective atimitating the natural upper airway muscle contraction function thattakes place during normal breathing. Normal breathing involves a complexinteraction of nerve and/or muscle stimulation that is precisely timedand is provided at precise stimulation levels so as to prevent airwaycollapse. Direct invasive, stimulation of the nerves and/or musclesassociated with the upper airway targets one nerve/muscle specifically,and, therefore, does not reproduce the overall neuromuscular function ofa normal human that is involved in maintaining airway patency duringnormal breathing. In addition, direct invasive stimulation of the nervesand/or muscles associated with the upper airway is considered to berelatively invasive medical procedure, and, therefore, may not befavored by a large number of patient's and/or caregivers.

It is also known to treat sleep apnea syndrome through surgical removalof tissues in the upper airway. In addition, pharmacological solutionshave also been pursued, at least with respect to the treatment ofcentral sleep apnea. However, neither of these therapies is successfulin all cases. Surgical removal of tissue is invasive, introduces apotential for complications, the long term effects are not known, and isonly marginally successful. Pharmacological therapy has been, ingeneral, less than satisfactory, and side effects are frequent.

There are many patients that suffer from sleeping disorders in additionto or other than sleep apnea syndrome. For example, many people havedifficulty falling asleep. Although the specific pathological reasonswhy some people have difficulty falling asleep are not believed to beknown, many phramacological solutions exist for assisting a person tofall asleep. However, such medications, which are essentially relaxants,may not be appropriate for some people, due to undesirable, known, orunknown drug interactions, for example, and, therefore, are disfavoredby some patients and/or caregivers. In addition, these medications mayproduce undesirable side effects, such as excessive drowsiness. Moreseriously, these medications may be contraindicated, and, therefore, ahealth risk.

It is also known that physically rocking the patient can be helpful ininducing sleep. To this end, beds with mechanical rocking mechanismshave been developed. It can be appreciated, however, that the rockingmotion may not be tolerated by the patient's bed partner. In addition,providing a bed that can rock an adult requires relatively costly,mechanically complicated, and potentially noisy rocking mechanisms tomove the bed in the desired rocking direction. In addition, such rockingbeds are typically cumbersome, aesthetically displeasing and notpractical in many homes.

Although not related to respiration or sleep, another disjunction ofinterest with respect to the present invention is vertigo and/ordizziness, which are disorders in which the sufferer has the sensationthat they or their surroundings are whirling. These disorders may beinduced by pathological reasons or from the physical movement of theuser, such as spinning in a disorienting fashion. Vertigo, for example,may also be the result of an inner ear disorder that effects thepatient's balance system. Depending on the underlying cause, treatmentof these disorders include physical therapy, cranial manipulation,surgery, and pharmacological intervention. However, some causes ofvertigo and/or dizziness have no cure or treatment. Furthermore, theexisting physical therapies, cranial manipulation treatments, andsurgeries are time consuming, may be only moderately effective, or areonly effective for specific types of diseases. Pharmacologicaltreatments can produce undesirable side effects and may not provideimmediate relief.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asystem that performs one or more of the following: augment or control apatient's respiratory function, open the patient's airway, induce sleep,and/or counteract vertigo that overcomes the shortcomings ofconventional treatment techniques. This general object is achievedaccording to principles of the present invention by providing avestibular stimulation system that stimulates at least a portion of thelabyrinth associated with the labyrinthine sense and/or at least one ofthe nerves in the inner ear associated with the labyrinthine sense, suchas the vestibular nerve and the branch nerves associated therewith. Thegeneral configuration for a vestibular stimulation system thataccomplishes this object includes a stimulation element that stimulatesthe targeted tissue, a stimulation power supply and control system thatprovides and controls the application of stimulation energy to thetargeted tissue via the stimulation device, and, in some applications,an input device, such as sensor, for providing input data to the controlsystem so that the control system can determine when and how to applystimulation energy to the patient via the stimulation element.Configurations for the stimulation system that performs the aboveidentified physiological functions are described briefly below.

Augmenting or controlling a patient's natural respiratory function isaccomplished by stimulating the vestibular nerve and/or one or morenerve branches associated with the vestibular nerve, either directly orindirectly, so as to induce a neural transmission in the vestibularnerve. Because of the interaction between the vestibular nerve and thenerves associated with respiration, such as the phrenic, hypoglossal,and recurrent laryngeal nerves, stimulation induced in the vestibularnerve induces stimulation in the nerves associated with respiration tocause or assist the patient in breathing. By inducing a neuraltransmission in the vestibular nerve, the vestibular stimulation systemcan be used to control one or more parameters associated with thepatient's respiration, such as set the start of inspiration, theduration and/or the force of the respiratory effort. For a patient thathas compromised respiratory effort, stimulating the vestibular systemcan be used to assist the patient's ventilation. If the patient isbreathing on their own, but not at an adequate level, stimulating thevestibular system can augment the patient's natural respiratory functionto increase the patient's respiratory effort. In one embodiment, thepresent invention contemplates using at least one sensor and a controlalgorithm or algorithms to synchronize triggering of the vestibularstimulation with the patient's respiratory cycle. However, the presentinvention also contemplates providing a time varying stimulation energyto at least a portion of the vestibular system irrespective of thepatient's respiratory cycle. In which case, the patient will synchronizehis or her respiratory cycle with this stimulation cycle.

Because stimulation of the vestibular nerve elicits stimulation in thehypoglossal, and recurrent laryngeal nerves, stimulating the vestibularsystem can also be used to maintain airway patency to treat OSA andupper airway resistance syndrome. Preferably, a sensor detects thepatient's respiratory cycle, such as by monitoring respiration, and thecontrol system applies stimulation to the vestibular system at anappropriate time, duration, and pattern during the respiratory cycle tomaintain the patency of the patient's airway.

Inducing or augmenting sleep is accomplished by rhythmically stimulatingthe vestibular system, such as the semicircular canal, saccule, utricaland/or ampullae, or the nerve branches associated with these structures,to produce a uniform rocking sensation in the patient. For example,locations on one or more of the semicircular canal(s), saccules, and/orutricles can be stimulated so as to cause a back and forth flow of thefluid in the semicircular canal to create the rocking sensation. Thisartificially created rocking sensation, like the actual rocking providedby a physically rocking the patient's bed, helps the patient relax andeventually fall asleep, as well as promotes sleep once the patient hasfallen asleep.

Countering vertigo and/or dizziness is accomplished by stimulating thevestibular system in a manner to as to mask out the signals from thevestibular system that would otherwise be interpreted by the brain as aspinning sensation. Preferably, a sensor detects the motion of thepatient and/or the unusual activity from the nerves in the inner ear andcauses the vestibular stimulation system of the present invention tocompensate for this motion and/or unusual neural activity by stimulatingthe vestibular system in such a manner so as to mask out the signalsindicative of spinning and/or the unusual neural signals. Thus,stimulating the vestibular system only takes place when the signals fromthe vestibular system would be interpreted by the brain as a spinningsensation and/or when the signals from the vestibular system are notnormal, which, if not treated, may cause the patient to experiencevertigo.

It is yet another object of the present invention to provide a method ofaugmenting or controlling a patient's respiratory function, opening thepatient's airway, inducing sleep, and/or counteracting vertigo that doesnot suffer from the disadvantages associated with conventionaltechniques for accomplishing these functions. This object is achieved byproviding a method that includes providing stimulation to the receptorsof the labyrinth associated with the labyrinthine sense and/or thenerves associated with such receptors, including the vestibular nerveand its branches.

For the method of augmenting or controlling a patient's respiratoryfunction and opening the patient's airway, this process, in oneembodiment of the present invention, includes sensing the condition ofthe patient, such as his or her respiratory cycle, and synchronizing thestimulation with the inspiratory phase in the case of augmenting therespiratory function. In another embodiment, a time varying stimulationenergy is applied to at least a portion of the vestibular systemirrespective of the patient's respiratory cycle, with the patientnaturally synchronizing himself or herself to this stimulation cycle. Inaddition, for opening the patient's airway, the method can includedetermining when conditions of the patient suggest that airway closingor cessation of breathing will occur and only provide vestibularstimulation if such conditions are present. For example, the stimulationsystem can detect when the patient is asleep, lying down, ceasesbreathing, or snores and begin the stimulation therapy only when one ormore such conditions exist.

For the method of inducing or promoting sleep, this stimulation processcan include applying stimulation to vestibular system, such as one ormore of the semicircular canals, ampullae, saccule and/or utricle, so asto produce a rocking sensation in the patient. In addition, this methodcan include sensing when the patient is in a preferred body position,such as supine, and/or sensing whether the patient is asleep or awake sothat stimulation to produce the rocking sensation is only initiated ifthe patient is supine and awake, for example. This method can alsoinclude providing the stimulation for a set duration, such as apredetermined period of time, following initiation of the stimulationtherapy so that the stimulation is applied to put the patient to sleep,but discontinues some time later, preferably once the patient has fallenasleep, much the same way a sleep timer on a radio or televisionfunctions to turn of the appliance after a set period of time. Ofcourse, the stimulation process can also continue throughout the sleepduration because the rocking sensation is believed to promote a restfulsleep for the patient even after the patient has fallen asleep.

For the method of counteracting vertigo, the vestibular stimulationprocess includes applying stimulation to the vestibular system in such amanner so as to mask out the signals from the semicircular canals thatwould otherwise be interpreted by the brain as a spinning sensation. Inaddition, this method can include sensing the motion of the patient sothat the masking stimulation is only applied if the patient is actuallyin motion.

These and other objects, features and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vestibular stimulation systemaccording to the principles of the present invention;

FIG. 2 is a side view of a human head showing the positioning of avestibular stimulation system using surface electrodes as a stimulatingelement according to one embodiment of the present invention;

FIG. 3 is a sectional view of a portion of the human anatomy showing theinner ear and schematically showing a vestibular stimulation systemaccording to one embodiment of the present invention;

FIG. 4 is a sectional view of a portion of the human anatomy alsoshowing the inner ear and schematically showing the location ofstimulation electrodes on the vestibular nerve and nerve branches;

FIG. 5 illustrates a portion of the inner ear showing additionalstimulation sites and stimulation elements;

FIG. 6 is a sectional view of a portion of the human anatomy showing theinner ear and schematically showing a vestibular stimulation system witha sensor provided in the patient's nasopharynx according to a furtherembodiment of the present invention;

FIG. 7 is a posteromedial view of the labyrinth and associated nervesshowing stimulation sites for augmenting/controlling the patient'srespiration according to the principles of the present invention;

FIG. 8 is another posteromedial view of the labyrinth and associatednerves showing stimulation sites for inducing sleep according to theprinciples of the present invention; and

FIGS. 9, 10, and 11 are schematic illustrations of alternativetechniques for stimulating a patient's vestibular system according tothe principles of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS OF THEINVENTION

FIG. 1 schematically illustrates an exemplary embodiment of a vestibularstimulating system 30 according to the principles of the presentinvention. Vestibular stimulating system 30 is a device that stimulatesportions of the labyrinth associated with the labyrinthine sense and/orassociated nerves to provide a therapeutic benefit to the patient. Morespecifically, the present invention contemplates stimulating, eitherinvasively or non-invasively, the receptors of the labyrinth associatedwith the labyrinthine sense and/or the nerves or nerve branchesassociated with such receptors, including the saccule, utricle,semicircular canals, vestibular nuclei, vestibular nerve and its nervebranches. The present invention contemplates providing stimulation to atleast one of these stimulation sites to perform one or more of thefollowing functions: a) augment or assist a patient's naturalrespiratory function, b) open the patient's airway, c) induce or promotesleep, and d) counteract vertigo. The details of the particular sites ofstimulation and the preferred stimulation mechanisms to achieve each ofthese functions are described below. However, a general description ofthe stimulation system of the present invention is first provided. Itshould be noted that the stimulation system of the present invention isreferred to through the present disclosure as a “vestibular stimulationsystem” because the stimulation sites of interest in the presentinvention are the above-identified structures and/or tissues of thehuman inner ear associated with the labyrinthine sense, which iscommonly referred to as the vestibular system.

As shown in FIG. 1, vestibular stimulating system 30 includes thefollowing three components: a stimulation element 32 that performs theactual stimulation of the tissue, a sensor 34 to detect a physiologicalcondition of the patient, and a power/control unit 36 that receives thesignals provided by sensor 34 and causes stimulation energy to beprovided to stimulation element 32 at an appropriate timing, level,pattern, and/or frequency to achieve the desired physiological function.As will become apparent, there may be instances where sensing aphysiological condition of the patient is not necessary in order todeliver the appropriate stimulation. For example, in one embodiment ofthe present invention, the stimulating system provides stimulation tothe patient regardless of the patient's condition or respiratory state.In which case, the sensor can be eliminated or simplified to an on/offswitch that activates and deactivates the supply of stimulation energyvia the power/control unit.

Stimulation element 32 is any device or combination of devices thatprovides a controlled stimulation to a target site. As noted above, theparticular stimulation sites of interest in the present invention areone or more of the following and/or a combination thereof: thevestibular nerve, portions of the vestibular nerve, the branches ofvestibular nerve or portions thereof, each of the semicircular canals(anterior, posterior, and lateral) or portions thereof, the common limb,utricle, saccule, and ampullae. It is to be understood that the precisestimulation site or sites, as well at the method in which the sites arestimulated, will vary depending on the physiological function to beachieved. Stimulation of each of these tissues can be provided on thesurface, internally, or in nearby tissues or structures. In addition,depending on the stimulation technique used, the stimulation devices canbe completely invasive, completely non-invasive, or a combinationthereof.

The present invention contemplates stimulating one or more of the abovestimulation sites using one or more of a variety of stimulationtechniques, such as electrical, mechanical, magnetic, thermal orchemical stimulation. The specific mechanism or combination ofmechanisms for delivering the stimulation will depend on the stimulationtechnique used, which will depend on the stimulation site selected. Thefollowing are examples of suitable stimulation techniques and theirstimulation mechanism that can be used in the vestibular stimulationsystem of the present invention to stimulate one or more of thestimulation sites identified above:

Electrical Stimulation—The present invention contemplates providingelectrically conductive electrodes in, on, and/or near the tissue to bestimulated so that an electric current can be delivered to the adjacenttissue via the electrode. The electrode or electrodes can have a varietyof sizes and configurations depending on the stimulation pattern to beprovided. For example, a point electrode can be used to stimulate a veryspecific site, or a spot or strip electrode can be provided to inducestimulation over a larger area. The present invention furthercontemplates providing electrical stimulating using a current controlledsource, in which the current output to the electrode is monitored. Thecurrent source automatically adjusts the current to keep it at or nearthe desired current level if, for example, the resistance of the patientchanges.

In addition, the present invention contemplates using a microstimulatorelectrode that is inserted at the stimulation site and that receivespower and control data from an external source, such as an rf fieldcreated by an external oscillator.

A specific type of a strip electrode that can be used in the presentinvention to stimulate a nerve is an electrode cuff that completely orpartially surrounds a nerve or nerve branch to be stimulated. Becausethe cuff surrounds to target nerve, it allows the stimulation energy tobe delivered through the nerve tissue while minimizing collateralstimulation of other tissues. Of course, multiple electrodes andelectrode pairs can be provided to achieve the desired stimulationpattern over the desired area to be stimulated. In addition, the presentinvention contemplates inserting one or more needle electrodes into theinner ear for selective simulation of a nerve, nerve branch, or a globalarea, such as the saccule, to promote the desired physiological effect.A needle electrode has the advantage of being able to target a specificlocation for stimulation.

Mechanical Stimulation—The present invention contemplates placing apressure application device, such as an inflatable balloon, near thetissue to be stimulated so that inflating the balloon applies a pressureon the adjacent tissue. This type of mechanical stimulation systemprovides pressure fluctuations to the patient to promote a particularsensation. Another example of a pressure application device particularlywell suited for use with the semicircular canal or with a nerve is apressure cuff, which is placed either completely or partially around thecanal or nerve to be stimulated so that inflating the pressure cuffexerts pressure on the underlying portion of the semicircular canal ornerve. Yet another mechanical stimulation device is a vibrating elementthat produces a mechanical vibration at a selected frequency.

Sonic Stimulation—The present invention also contemplates stimulatingthe vestibular area or specific sites within this area using a sonic orultrasonic device that delivers stimulation on a carrier wave typicallyabove 20,000 Hz, which is not in the audible range for humans.

Magnetic Stimulation—The present invention further contemplatesproviding a magnetic field generator in the form of one or more coils inand/or near the inner ear. The coils generate a time varying magneticfield that creates a spatially varying electric field that inducesstimulation in the target tissue. In addition, focusing elements, suchas ferromagnetic material implants, can be provided in or near thetargeted tissue to focus or shape the magnetic field, and, hence theelectric field, at a specific location.

Thermal Stimulation—The present invention contemplates providing astimulation device that uses changes in temperature to inducestimulation of the patient's tissue. Examples of devices that induce atemperature change include a laser, infrared device, or a device thatdispenses heated or chilled liquid to the stimulation site.

Chemical Stimulation—The present invention further contemplatesproviding a device that introduces chemicals or that causes chemicalreactions at a stimulation site to control the stimulation at that site.For example, an injection or medicine pump can be provided at the innerear to introduce the desired stimulation medication at the stimulationsite.

Radio-Frequency Stimulation—The present invention still furthercontemplates using radio frequency wavelengths generated by a suitabledevice to provide the desired stimulation. For example, as noted above,stimulation can be induced by providing power and control data usingradio frequencies (rf) received by one or more microstimulatorsimplanted in the patient. Different microstimulators implanted atdifferent locations in the patient can be tuned to different frequenciesso that a wide variety of stimulation patterns can be achieved.

Infrared Stimulation—The present invention also contemplates usinginfrared technology to deliver the stimulation to the patient's tissues.Short wave, 7,200-15,000 Å, or long wave, 15,000-150,000 Å, systems canbe used to deliver the stimulation to the target site.

It is to be understood that this list of stimulation techniques is notexhaustive or exclusive. On the contrary, the present inventioncontemplates using any stimulation technique or device that, whenactuated, provides the desired stimulation function. The selection anddifferent types of suitable stimulation devices suitable for use inachieving the desired physiological function of the present inventionwill be better understood from the discussion of the particularimplementations of the stimulation system of the present inventionprovided below.

Sensor 34 is a device that detects a physiological condition of thepatient or the external conditions that the patient is experiencing andprovides this information to power/control unit 36. It can beappreciated that the specific type of sensor used with the stimulationsystem of the present invention to monitor one or more of theseparameters will depend on the parameter of interest. Nevertheless,examples of suitable sensors for use with the present inventioninclude: 1) a pressure sensor that detects a pressure of a fluid, 2) aflow sensor that detect a flow of a fluid, 3) an effort sensor thatdetect expansion and contraction of the thorax, 4) an oximeter, 5) atemperature sensor, 6) a microphone, 7) a nerve activity or conductionsensor, 8) an EMG sensor, 9) an EEG sensor, 10) an EOG sensor, and 11)an accelerometer. Details of how each of these sensors is optimally usedin conjunction with the vestibular stimulation system of the presentinvention are provided below.

It is to be understood that this list of suitable sensors is also notexhaustive or exclusive. On the contrary, the present inventioncontemplates using any sensor that is capable of detecting or monitoringa characteristic of the patient of interest, such as the patient'srespiratory cycle, and that provides a signal indicative thereof. Aswith stimulation element 32, the selection and different types ofsuitable sensors for use with each embodiment of the present inventioncan be appreciated from the discussions of the particularimplementations of the stimulation system of the present invention.

Power/control unit 36 is any device that provides stimulation energy tothe patient via the stimulation element and that is capable ofcontrolling the application of this energy. For example, power/controlunit 36, is, in one embodiment of the present invention, a rechargeablebattery with a pulse shaping device that modulates the shape, frequencyand amplitude of pulses of stimulation energy provided to thestimulation element by the battery. The power/control device preferablyalso includes a processor that is capable of receiving signals fromsensor 34 and controlling the application of stimulation energy, i.e.,the shape, time, frequency, and/or amplitude of the pulses applied tothe stimulation element, based on the input signals from sensor 34 toachieve the desired physiological function. Of course, if sensor 34 iseliminated, the power/control device provides the stimulation energyaccording to predetermined criteria.

The present invention contemplates that power/control unit 36 caninclude an “intelligence” capability that provides relatively complexcontrol functions, such as adaptively controlling the stimulationenergy, compensating for changes in monitored parameters, allowing theuser to specify the control ranges, and detecting between events ofinterest, such as respiration and snoring, and noise. For example, in anexemplary embodiment of the present invention, the user or manufacturerprovides the power/control unit with the stimulation parameters, such asintensity, frequency, interpulse duration, for the stimulation energy tobe provided to the patient. Thereafter, these parameters are changeableby the patient or adaptively changeable by the control unit so that thetarget nerve firing rate is controllable to create the desiredstimulation function.

A variety of control techniques can be used to provide this intelligentcapability, such as fixed parameter control where the control unitcauses a certain action if a particular parameter is detected, thresholdbased control where the control unit compares an input signal to athreshold to determine if an action is required, rule based control,fuzzy logic, and neural network control. Power/control unit 36 can beprovided outside the patient, entirely within the patient, or acombination thereof. Details of the function of the power/control unitto control the stimulation energy provided to the patient and specificexamples of this device are discussed below.

FIGS. 2, 3 and 4 illustrate exemplary embodiments of vestibularstimulation systems 30. In FIG. 2, vestibular stimulation 30 is acompletely non-invasive system in that no part of the system is disposedin the patient. Vestibular stimulation system 30 in FIG. 2 includes astimulation element 33 in the form of a surface electrode that isdisposed on the surface of the patient just behind the ear so that theelectrode generally overlies the vestibular system. The remainingportions of the stimulation system, such as the power supply and thecontrol unit 36, are worn on the ear in the same manner as aconventional hearing aid. When activated, the power supply and controlunit 36 energize electrode 33 to send a stimulating current to thepatient's vestibular system.

In FIG. 3, vestibular stimulation system 30′ is an invasive system thatdirectly stimulates the vestibular nerve and/or its branches. Vestibularstimulation system 30′ of FIG. 3 includes stimulation elements 38 and40, which are electrodes placed directly on or near vestibular nerve 42and branch nerves 44 that lead to the vestibular nerve. The presentinvention contemplates that electrodes 38 and/or 40 can be positionedrelative to the vestibular nerve 38 and/or a branch nerves 44 associatedtherewith, respectively, at a variety of locations along these nerves ornerve branches, so long as they are positioned so as to inducestimulation in the associated nerve. For example, electrode 38 can beprovided on vestibular ganglion 41. Branch nerves 44 are the nervescoupled to the receptors of the labyrinth associated with thelabyrinthine sense, such as the semicircular canals 46 a, ampullae 46 b,utricle 46 c, and saccule 46 d. Note that the semicircular canals,ampullae, utricle, and saccule are generally identified by numeral 46 inFIG. 3, but are shown in greater detail in FIG. 4. Branch nerves 44combine to form vestibular nerve 42.

FIG. 4 illustrates in better detail the inner ear and the placement ofelectrodes 40 a-40 e on branch nerves 44 and the placement of electrode38 on vestibular nerve 42. Electrodes 40 a-40 e are generallyillustrated in FIG. 3 as electrodes 40. It is to be understood that thenumber of electrodes and their locations can vary and that electrodestimulators need not be placed on each branch nerve. For example,electrode 38 on vestibular nerve 42 or one or more electrodes 40 a-40 eon branch nerves 44 may be eliminated if the desired stimulation effectis achieved by stimulating another nerve or nerves. Ideally, the numberof electrodes should be kept to a minimum while providing the desiredstimulation effect.

Referring again to FIG. 3, in the illustrated exemplary embodiment,power/control unit 36 of vestibular stimulation systems 30′ includes asignal receiving device 48 implanted in tympanic cavity 50 on theinterior side of eardrum 52. A signal generator 56 is provided on theexterior side of eardrum 52 in ear canal 58. One or more leads 54 couplesignal receiving device 48 to each of electrodes 38 and/or 40 so thateach electrode can be energized individually or in any combination. Forexample, this configuration allows for simultaneous stimulation ofmultiple electrodes at multiple sites based on a common stimulationsource from signal receiving device 48. In addition, this configurationallows for independent control of one or more of the electrodes toprovide a great degree of flexibility for the different types ofstimulation patterns that can be applied to the patient's vestibularsystem. For example, the present invention contemplates stimulatingbetween sites, for example, from 40 a to 40 b, 40 a to 40 c, 40 b to 40c, etc.

Signal generator 56 communicates with signal receiver 48 to cause signalreceiver to provide stimulation energy to stimulation electrodes 38and/or 40. In an exemplary embodiment of the present invention, signalgenerator 56 generates an electromagnetic field that induces a currentin signal receiving device 48, which is then transmitted to electrodes38 and/or 40. If, however, signal receiving device 48 is provided withits own power supply, the signals from signal generator 56 are commandand control signals that dictate how and when the stimulation energy isoutput from signal receiving device 48. It should be noted that signalgenerator 56 need not be provided within the ear canal, as shown, if itstransmission range is sufficient to transmit greater distances.

The present invention also contemplates doing away with signal receivingdevice 48 and leads 54 in favor of having an electromagnetic fieldproduced by signal generator 56 directly induce stimulation pulses atthe electrodes or at the stimulation site. For example, magneticstimulation can be used to induce stimulation in the target tissue. Inwhich case, the coil or coils that generate the magnetic field functionas signal generator 56, and electrodes 38 and/or 40 can be eliminated.Alternatively, ferromagnetic devices that shape the fields generated bythe can be provided at or near the stimulation sites to function in muchthe same capacity as electrodes 38 and/or 40 to ensure that the targetsite is adequately and properly stimulated.

The present invention also contemplates that one or moremicrostimulators, which receive power and data from an external sourcevia rf frequencies, can be implanted in the patient to function aselectrodes 38 and/or 40. In which case, the rf oscillator functions assignal generator 56 and is located externally relative to the patient,such as at the patient's bedside.

A power/control unit 60, similar if not identical in function topower/control unit 36 discussed above, causes signal generator 56 toproduce the electromagnetic field or other coupling mechanism thatinitiates stimulation. In the illustrated embodiment, at least onesensor 34 communicates with power/control unit 60 to provide an inputsignal that is used by the control unit to determine when to generatethe electromagnetic field. As discussed in greater detail below, thespecific type of sensor or sensors used, and how the control unit usesthe received signals to provide stimulation energy to the stimulationelements 38 and/or 40 will depend on the physiological function to beachieved as a result of the stimulation of the vestibular system.Power/control unit 60 is preferably provided outside the patient tosimplify recharging or replacing the power supply. Sensor 34 is alsotypically provided outside the patient. However, sensor 34 may beimplanted within the patient if the parameter being monitored requiresand/or allows for an invasive location for the sensor.

As noted above, the present invention contemplates stimulating one ormore locations in the inner ear associated with the labyrinthine sense,in addition to or in place of direct stimulation of the vestibular nerveand its branches, as shown in FIGS. 2, 3 and 4, in order to provide atherapeutic benefit. That is, it is not necessary that the vestibularnerve or its branches be directly stimulated in order to induce a neuraltransmission in the vestibular nerve. Because the vestibular nerve is anafferent nerve, and stimulating anything before it involvestransduction, stimulation can be provided at one or more sites beforethe vestibular nerve and still induce the desired neural transmissiontherein. It should be noted that the term “before” as used in thisparagraph refers to portions of the nerve in a direction opposite thedirection of normal neural conduction.

FIG. 5 illustrates a portion of the inner ear showing additionalstimulation sites that, once stimulated, induce a neural transmission inthe vestibular nerve to provide a therapeutic benefit to the patient.The basic components of the stimulation system shown in FIG. 5 are thesame as those illustrated in FIGS. 2-4 except for the stimulation sites.For the sake of illustration, a variety of stimulation devices servingas stimulation element 32 are shown in this embodiment of the presentinvention. For example, FIG. 5 illustrates a pair of cuffs 62 a and 62 bspaced apart from one another and each surrounding a portion of theposterior semicircular canal 46 a′. Cuffs 62 a and 62 b can beelectrodes or pressure application devices that exert a force on thesemicircular canal. In addition, FIG. 5 illustrates electrodes orpressure application devices 64, 66 and 68 provided on an ampulla 46 b,and portions of utricle 46 c for stimulating these structures. Inaddition, FIG. 5 illustrates electrodes or pressure application devices70 and 72 provided on either side of posterior semicircular canal 46 a′.It is to be understood that the present invention contemplatesstimulating the outside of the semicircular canals, as shown, as well asstimulating within the semicircular canals. Lead or leads 54 couplesignal receiving device 48 to each of these stimulation elements toprovide the appropriate stimulation energy or impetus, such as a currentin the case of an electrode or an inflating fluid in the case of apressure application device.

The configuration for vestibular stimulation system 30, 30′ shown inFIGS. 2-5 is advantageous in that it minimizes the number and complexityof components that are provided within the patient. It is to beunderstood that the present invention contemplates that the power supplycould include one or more miniature batteries implanted within thepatient, rather than the current coupling system shown in the figures.Such an implanted battery system, however, increases the amount offoreign objects that must be disposed within the patient. In addition,if it became necessary to replace the batteries at some point in thefuture, an additional surgery would be required.

The configuration for vestibular stimulation system 30, 30′ shown inFIGS. 2-5 is further advantageous in that no elements of the system arepenetrating the patient's tissues from an internal to external location.It is to be understood that the present invention contemplateseliminating signal receiving device 48 and extending leads 54 outsidethe body, such as through the eardrum or through the surrounding tissue,for providing energy to the electrodes. Alternatively, the presentinvention contemplates that electrodes 38 and/or 40 are relatively stiffneedle electrodes that insert through the eardrum, for example, with thedistal end remaining outside the patient. In these configurations, leadsor electrodes must physically pass from an interior location within thepatient to an exterior location so that they can be coupled to thepower/control unit. While this embodiment provides a good path ofconduction for the stimulation energy and minimizes the amount offoreign objects located within the patient, when a foreign objectextends through the patient's tissue, providing a path from the interiorto the exterior of the patient, this represents a potential site forinfection or provides a pathway by which infections may enter the body.

While FIGS. 2, 3, and 4 illustrate an electrode stimulation system, itis to be understood that any of the above-described stimulationtechniques can be employed to stimulate the patient's vestibular system.For example, electrodes 38 and/or 40 can be replaced with pressure cuffsto apply a physical pressure on the vestibular sensory tissue. As willbe understood from the following discussions of the physiologicalfunctions that can be achieved by the stimulation system of the presentinvention, the present invention contemplates stimulating sites withinthe inner ear other than or in addition to the nerve stimulation sitesshown in FIGS. 2, 3, and 4. For example, the same stimulation effectaccomplished by stimulating the vestibular nerve directly may beaccomplished by globally stimulating the portions of the labyrinthassociated with the labyrinthine sense. Please refer to FIG. 5 for adiscussion of other exemplary stimulation sites of the presentinvention.

Augmenting and/or Controlling a Patient's Respiratory Function

In one embodiment of the present invention, vestibular stimulationsystem 30, 30′ is used to accomplish the physiological function ofaugmenting the respiratory effort of a patient. This is accomplished bystimulating the vestibular nerve either directly, as shown in FIGS. 3and 4, or indirectly, as shown in FIGS. 2 and 5, in synchronization withthe patient's respiratory cycle. Details of this embodiment arediscussed below with reference to FIGS. 2-7.

As noted above, vestibular nerve 42 is connected polysynaptically to thephrenic nerve, abdominal nerve, hypoglossal nerve, and the recurrentlaryngeal nerve, all of which are associated with the musculature of therespiratory system. For this reason, stimulating the vestibular nervehas the effect of stimulating, on a macro level, all of these otherrespiratory-related nerves. This, in turn, induces or augments thecontraction of the respiratory muscles, thereby supporting or augmentingthe overall respiratory function of the patient. By varying thestimulation level of the vestibular system, the present invention cancontrol the degree of ventilatory assistance provided to the patient.

As noted above, stimulating the vestibular system in this mannerprovides a macro stimulation of many, if not all, of the respiratorymuscles, such as the diaphragm and intercostal muscles, while targetingthe stimulation at a relatively small site. Conventionalelectroventilation systems, on the other hand, target the phrenic nerve,portions of the phrenic, or the respiratory muscles directly, see, e.g.,U.S. Pat. No. 4,827,935 and the article by Geddes et al. entitled,“Electrically Produced Artificial Ventilation” published in 1988 atpages 263-271 in vol. 22, no. 6, of a periodical entitled MedicalInstrumentation. As a result, these electroventilation techniquesprovide only a micro-stimulation of one component of the overallphysiology associated with providing a respiratory effort.

In one embodiment of the present invention, the application of thestimulation energy to the vestibular system is synchronized with thepatient's respiratory cycle. In this embodiment, sensor 34 in vestibularstimulation system 30, 30′ is any device, apparatus or system that iscapable of detecting and/or monitoring the respiratory cycles of aspontaneously breathing patient and that can be used to discern betweenthe inspiratory and the expiratory phases of the respiratory cycle. Forexample, the present invention contemplates detecting the flow,pressure, or volume of fluids delivered to or inspired by the patientduring breathing. Detecting these parameters associated with thepatient's breathing can be accomplished, for example, using a pneumotachflow meter in communication with the patient's airway. This informationcan then be processed by control unit 60 using well known techniques todetermine the phase of the respiratory cycle.

The present invention also contemplates detecting sounds of thepatient's breathing to discern when the patient is breathing in and out.In addition, the present invention contemplates detecting patientmovement, such as the rise and fall of the chest, via sensor 34 todetect the inspiratory and the expiratory phases of the respiratorycycle. Numerous techniques, such as resistance or inductance belts,pressure sensors, and impedance pneumography, are known for detectingsuch movement of the patient. Other suitable sensors that detect patientrespiration include a temperature detecting system that detectstemperature variations associated with a patient's respiration. Forexample, it is known to provide a thermister at or near the patient'sairway to detect the heat associated with the expired air from thepatient. Thus, when heat is detect by such a sensor, this indicates thatthe patient has reached the expiratory phase of the respiratory cycle.See, for example, U.S. Pat. Nos. 5,190,048 and 5,413,111 both toWilkinson, the contents of which are incorporated herein by reference.In addition, sensor 34 in this embodiment can detect theelectrical/neural activity of a patient associated with a patient'srespiration, such as the EMG signal from the diaphragm to detectinspiration and expiration.

In this embodiment, stimulation is provided to the vestibular system insynchronization with the patient's breathing, so that stimulation ofvestibular nerve 42 occurs at an appropriate time to coincide with theonset of an inspiration, thereby augmenting the patient's naturalbreathing. It can be appreciated that synchronizing the stimulation withthe patient's inspiration may require initiating the process ofproviding stimulating energy prior to the commencement of theinspiratory phase to account for any time lag introduced by thestimulation system and any physiological lag time, such as the time itmay take for the stimulation energy to induce a stimulation in thetarget tissue and the time it may take for the excitation of thevestibular nerve to travel to the portions of the body, such as thebrainstem, where it induces a stimulation in the nerves associated withrespiration.

In another embodiment of the present invention, stimulation of the atleast a portion of the vestibular system is provided irrespective of thepatient's own respiratory cycle or efforts. Instead, stimulation energyis applied continuously in a time varying fashion, such as in the formof a sine wave. The patient will naturally synchronize their ownrespiratory cycle with that of the stimulation cycle. This represents asignificant simplification over a stimulation system that attempts tosynchronize the application of stimulation with the patient'srespiratory cycle, in that sensor 34 and its feedback functions areeliminated. Yet, this embodiment of the present invention effectivelyaccomplishes the respiration augmentation or control function, becausethe patient will naturally adjust their own respiratory pattern to matchthe stimulation pattern being applied to the vestibular system by thevestibular stimulation system.

In an exemplary configuration for this embodiment of the presentinvention, stimulation is provided directly to vestibular nerve 42and/or to the branch nerves 44. See FIGS. 3 and 4, which illustrate asystem for stimulating these nerves. FIG. 5 also illustrates the humaninner ear with a direct simulation of vestibular nerve 42 via electrode38 using signal receiving device 48. In the embodiment illustrated inFIG. 6, however, a pressure sensor 74 is provided in the nasopharynx 76and communicates with signal receiving device 48 via a communicationwire 78 that extends along the pharyngotympanic (auditory) tube 80, alsoreferred to as the eustachian tube, between tympanic cavity 50 andnasopharynx 76. By being situated in the nasopharynx, pressure sensor 74detects pressure changes in the patient resulting from respiration,upper airway dysfunction and swallowing. Of particular interest isdetecting pressure changes resulting from respiration, so that theoutput from the sensor can be used as an input signal to trigger thevestibular stimulation.

While FIG. 6 illustrates pressure sensor 74 as being provided in thenasopharynx, it is to be understood that the pressure sensor could beprovided at other locations, such as in the pharyngotympanic, so long asthe sensor detects pressure changes in the upper airway region. Inaddition, other types of sensors in addition to or in place of pressuresensor 74 can be provided in communication with the patient's upperairway via the eustachian tube. For example, a microphone can beprovided to detect respiration and/or snoring. In addition, the sensoror sensors in the nasopharynx and/or eustachian tube can communicatewith another device, such as signal receiving device 48, wirelessly.

In one variation of this embodiment, signal receiving device 48communicates with signal generating device 56, as indicated by arrow A,to transmit information regarding patient respiration from signalreceiving device 48 to signal generating device 56, which is based onthe output from pressure sensor 74, so that power/control unit 60provides the appropriately timed stimulation energy to the vestibularsystem. Another variation of this embodiment contemplates that thesignal receiving device itself controls the application of stimulationenergy to the vestibular system based on the output from pressure sensor74. In which case, a constant supply of stimulation energy is preferablydelivered by signal generating device 56 to signal receiving device 48so that stimulation energy is always available when signal receivingdevice 48 determines that stimulation is to be applied.

In the embodiment shown in FIG. 6, power/control unit 60 is preferablyworn behind the ear, with a lead 61 coupling the power/control unit tosignal generating device 56 much in the same way a number of typeshearing aids are currently used, It is to be understood, however, thatthe present invention contemplates locating power/control unit 60anywhere on or near the patient so long as it functions for its intendedpurpose of providing a controlled supply of stimulation energy to thestimulation element(s).

While FIGS. 3 and 6 shows lead 54 as apparently passing through thecochlea, it is to be understood that this is preferably not the case.Lead 54 is shown overlying the cochlea for ease of illustration.Preferably, lead 54 is directed in a path from signal receiving device48 to the stimulation electrode that minimizes damage to the patient'stissues.

FIG. 7 is a posteromedial view of the labyrinth and associated nervesshowing presently preferred stimulation sites according to theprinciples of the present invention for this embodiment. In thisembodiment, augmenting the respiratory function is accomplished byinducing stimulation of the vestibular nerve so that the polysynapticinteraction of the vestibular nerve with the nerves associated withrespiration can augment the patient's respiratory function. Thus, aprimary function of the vestibular stimulation system is to induce astimulation of the vestibular nerve. This is accomplished according toan exemplary embodiment of the present invention, as shown in FIG. 7, bystimulating vestibular nerve 42 directly and/or by stimulating one ormore of nerve branches 44 a and 44 b. For example, an electrode 82 indirect contact with vestibular nerve provides the stimulation to thisnerve. A lead 84 couples the electrode to the source of stimulationenergy. Of course, lead 84 can be eliminated if stimulation energy isinduced by the electrode itself, for example, by using a microstimulatoras electrode 82, which is powered and controlled by an rf coupling. Inaddition, stimulation can be provided non-invasively, i.e., without lead84 or electrode 82, using, for example, magnetic stimulation, in which atime-varying magnetic field is generated that creates a spatiallyvarying electric field gradient to induce stimulation of the targetarea. Alternatively, or in addition to electrode 82, the presentinvention contemplates providing electrodes 86 a and 86 b in contactwith nerve branches 44 a and 44 b, respectively, to stimulate the nervebranches, which, in turn, induce stimulation in the vestibular nerve.Leads 54 a and 54 b couple electrode 86 a and 86 b to the source ofstimulation energy. Of course these leads can be eliminated as discussedabove with respect to lead 84.

It is to be understood that the physiological function of augmenting therespiratory function of this embodiment of the present inventioncontemplates stimulating portions of the vestibular system before thevestibular nerve or nerve branches to induce a neural transmissiontherein. Thus, this embodiment of the present invention alsocontemplates stimulating the structures of the vestibular system, suchas the semicircular canals 46 a, ampullae 46 b, utricle 46 c, saccule 46d, and common membranous limb 46 e using any of the above-describedstimulation mechanisms. In addition, the present invention contemplatesglobally stimulating the vestibular area in synchronization withbreathing to augment the patient's respiratory function.

In the above embodiment of the present invention, the vestibular systemis used to augment the patient's respiratory function by in effect“boosting” the stimulation of the respiratory muscles via a stimulationapplied to or induced in the vestibular nerve. In one embodiment of thepresent invention, this includes sensing the patient's respiration andappropriately timing the application of the stimulation energy tocoincide with the respiratory cycle of the patient. However, as notedabove, the present invention also contemplates controlling the patient'sventilation based on stimulation of the vestibular system. For example,instead of augmenting whatever respiratory function the patient mayhave, the stimulation system of the present invention takes over theresponsibility of initiating or inducing inspiration. Such a system isparticularly suited for patients suffering from central sleep apnea. Forexample, the present invention contemplates monitoring the patient'srespiration, and once a cessation of breathing for a predeterminedperiod of time is detected, vestibular stimulation is applied to induceor initiate inspiration.

In addition, the present invention contemplates providing appropriatealarms and other monitoring functions to monitor the patient an/or thecondition of the stimulation system and communicate the monitoredinformation to a caregiver and/or to a storage device, so that emergencyconditions, such as failure of the vestibular stimulation system can bedetected and reported. In addition, information on the use and functionof the stimulation system can be obtained and recorded.

Maintaining Airway Patency

It is generally understood that relaxation of the muscles associatedwith the upper airway, such as the genioglossus, is a contributingfactor, if not a primary factor, in the occurrence of obstructive sleepapnea for many individuals. It as also been found that tensing theseupper airway muscles, at least during the inspiratory phase of therespiratory cycle, minimizes collapse of the upper airway. Thus, afurther embodiment of the present invention contemplates reducing orminimizing the occurrence of OSA or upper airway resistance by tensingthe upper airway muscles during at least the inspiratory phase of therespiratory cycle. It can be appreciated that because stimulation of thevestibular nerve elicits firing of the hypoglossal nerve and therecurrent laryngeal nerve, which are the primary nerves associated withthe muscle groups in the upper airway, stimulating the vestibular nervealso tenses the upper airway muscles, thereby minimizing collapse of theupper airway. Thus, the present invention contemplates stimulating thevestibular system to minimizing collapse of the upper airway.

Preferably, stimulating the vestibular nerve to maintain airway patencyis done in the manner discussed above with respect to stimulating thisnerve to augment the patient's respiratory function, e.g., bystimulating the nerve directly or by stimulating tissues or nervebranches before the vestibular nerve, and using any of the stimulationtechniques and mechanisms discussed above. In addition, stimulation ispreferably synchronized with the inspiratory phase of the respiratorycycle, because it is during this phase that the negative pressure in theairway tends to urge the unsupported or under-supported airway tocollapse. Therefore, the control systems and techniques discussed aboveare equally applicable to the use of the vestibular stimulation systemfor maintaining airway patency.

The present invention contemplates initiating the stimulation therapy tomaintain airway patency based on an event, such as when the patientactivates the therapy system or when the patient lies down to sleep,based on a timer, such as initiating the therapy at a set time periodeach night or some duration after the patient initiates a start oftherapy or upon going to sleep. Once initiated, the stimulation therapycan be provided throughout the night. However, the present inventionalso contemplates providing the stimulation therapy to maintain airwaypatency only if conditions suggest that the patient is experiencing orlikely to be experiencing an apnea or even a hypopnea. For example, thepresent invention contemplates initiating the stimulation therapy onceit is determined that the patient is experiencing an apnea. This can bedone using any conventional technique, such as by monitoring respiration(respiratory movement of the patient), respiratory flow, and/or oxygensaturation. The present invention also contemplates using snore to beginthe stimulation therapy.

In addition, the present invention contemplates controlling thestimulation energy based on the severity of the patient's condition. Forexample, if apneas and/or snoring continue even after the stimulationtherapy begins, the present invention contemplates increasing thestimulation level. Conversely, if apneas and/or snoring diminish, thestimulation level is reduced.

Preferably, stimulation energy is provided to the vestibular systemprior to the onset of inspiration so that the muscles associated withthe upper airway are contracting or beginning to contract before theinspiratory force increases to a level that would otherwise cause theupper airway to collapse. One reason for providing stimulation beforethe start of inspiration is to counteract the collapsing forces that acton the upper airway during inspiration. For example, once inspirationcommences, a negative pressure is developed in the airway. This negativepressure tends to cause the airway to collapse or reduce in crosssectional area. It is believed that once the airway has collapsed, it isdifficult, if not impossible, to overcome the collapsing forces.

In addition, to prevent airway collapse in the first place, it isbelieved to be preferable to make the cross-sectional area of the airwayas large as possible before inspiratory flow begins in the airway. Itcan be appreciated that a reduction in the cross-sectional area of theairway increases the resistance to inspiratory flow, which, in turn,increases the negative pressure in the airway that urges the airway tocollapse. If vestibular stimulation is applied prior to inspiration, themuscles associated with the airway are tensed, thereby preventing areduction in the cross-sectional area to minimize the resistance to airflow. Minimizing the resistance to airflow improves airflow, therebyreducing negative pressure that potentially causes the airway tocollapse. For these reasons, the present invention induces contractionin the muscles associated with the upper airway before a collapsingforce, such as the negative pressure developed during inspiration, hasthe opportunity to cause the airway to collapse.

As noted above, in some patients, once a collapse or reduction in theairway has taken place, it is relatively difficult to open the airway byinducing contraction in the upper airway muscles. It is postulated thatonce airway collapse has occurred, the amount of tissue mass that mustbe moved is prohibitively large. In addition, if the patient is lyingdown, gravity tends to urge the tissues to collapse into the airway, sothat opening the airway also requires overcoming the effects of gravity.Also, the action of the respiratory muscles in attempting to continuerespiration may cause a vacuum to be created that tends to urge theairway tissues together, thereby making it especially difficult for anelectrically induced contraction to be effective in opening the airway.Furthermore, the mucus-like characteristics of airway may cause asealing effect, that also makes it especially difficult for anelectrically induced contraction to be effective in opening the airway.Therefore, it is preferable to initiate stimulation prior to the onsetof inspiration.

A primary difference between using the vestibular stimulation system ofthe present invention to augment or control the patient's respiratoryeffort and using the vestibular stimulation system to maintain airwaypatency is that the latter physiological function of maintaining airwaypatency is accomplished on an otherwise healthy patient that does notneed ventilatory assistance. That is, the same basic system thatmonitors the respiratory cycles of a patient and stimulates thevestibular system in synchronization with the respiratory cycle can beused to either 1) augment the respiratory function if the patientrequires ventilatory assistance or 2) maintain the opening of the airwayif the patient suffers from OSA or upper airway resistance syndrome(UARS). Of course, both functions are accomplished if the patientsuffers from OSA or UARS and requires ventilatory assistance.

Controlling/Pacing Respiration

The present invention also contemplates that the amount of stimulationapplied to the vestibular system can be varied to control the force andduration of the inspiratory or expiratory effort. For example, it isknown that taking a deep sigh once in a while is beneficial torespiration. Thus, the vestibular stimulation system of the presentinvention can be used on induce a deep sigh during the inspiratory phaseof the respiratory cycle.

As noted above, the present invention contemplates that thepower/control system can provide stimulation to the patient to serve asa diaphragm pacing device. For example, in some patients the ability toaccurately and reliably trigger the respiratory cycle may be degraded orlost. Stimulating the vestibular nerve, either directly or indirectly,because it elicits a direct response in the phrenic nerve can be used tostart and/or control the patient's inspiration. This embodiment issimilar to the use of the vestibular stimulating system to treat centralsleep apnea, where the stimulation device provides stimulation to thevestibular system if the patient has not initiated inspiration on theirown after a certain amount of time elapses.

It can be appreciated that controlling the patient's ventilationrequires providing timing logic in power/control unit 60 so that thestimulation energy is provided to the vestibular system in a cyclicalfashion and so that the stimulation energy is provided for the properduration. It is to be understood that the power/control unit can beprogrammed to vary the pattern for the patient's respiratory cyclerandomly, which is known to enhance the ventilation function. It is tobe further understood that the techniques that are used to controlconventional electroventilation device can be used to control thevestibular stimulation system of the present embodiment. The differencebeing that, in the present invention, the electrical stimulation isprovided to the vestibular system to accomplish the macro stimulation ofmany, if not all, of the neural-muscular systems associated withrespiration, rather than one specific component thereof, such asstimulating the diaphragm.

Inducing or Promoting Sleep

A further embodiment of the present invention contemplates providingstimulation to the appropriate portions of the vestibular system in anappropriately timed fashion so as to produce the sensation of rocking inthe patient. It is believed that this rocking sensation produced from anartificial stimulation of the vestibular system, just as with physicallyrocking the patient, will induce sleep in the patient and, for asleeping patient, will promote a more restful sleep.

In one embodiment of the present invention, the sensation of rocking isinduced by stimulating one or more of the semicircular canals, saccules,and/or utricles. For example, FIG. 8 illustrates a first stimulationelement 88 provided at a first location on semicircular canal 90 and asecond stimulation element 92 provided at a second location on the samesemicircular canal. First and second stimulation elements 88 and 92 areoperatively coupled to a signal receiving device for controlling theapplication of stimulation to semicircular canal 90. In one embodiment,stimulation elements 88 and 92 are electrodes, such as cuff electrodesdiscussed above, for providing electrical energy to the patient from asource. Leads 94 and 96 couple the electrodes to the power supply.

In another embodiment, first and second stimulation elements 88 and 92are pressure application devices, such as the pressure cuffs discussedabove, that apply a pressure to the semicircular canal. In which case,leads 94 and 96 are conduits for carrying an inflating fluid to thepressure cuffs. In yet another embodiment, first and second stimulationelements 88 and 92 are pressure application devices located within thesemicircular canal for moving the fluid contained therein. In stillanother embodiment of the present invention, stimulation of the canalsis accomplished via one or more vibrating elements located proximate tothe semicircular canal, such as in the bone tissue adjacent the duct inwhich the semicircular canal is located.

In this embodiment, a rocking sensation is induced in the patient byalternatively actuating first and second stimulation elements 88 and 92.For example, if first and second stimulation elements 88 and 92 arepressure cuffs, first stimulation element 88 is actuated and secondstimulation element 92 is deactivated to tend to urge the fluid withinsemicircular canal 90 in a first direction toward the second stimulationelement, as indicated by arrow B. Thereafter, first stimulation element88 is deactivated and second stimulation element 92 is actuated to urgethe fluid in the opposite direction back toward the first stimulationelement, as indicated by arrow C. This process can be repeated to movethe fluid back and forth within the semicircular canal, which is thesame effect that takes place when the person is physically rocked. Ofcourse, the frequency of the back and forth movement of the fluid can bealtered to change the rocking speed of the patient.

It is to be understood, that the placement of first and secondstimulation element 88 and 92 on semicircular canal 90, which is theposterior semicircular canal, may not be the optimum location for allpatients. Thus, the present invention contemplates locating the firstand second stimulation element on other semicircular canals, such asanterior semicircular canal 98 and/or lateral semicircular canal 100. Itis to understood that such stimulation elements can be provided at oneor more of these semicircular canals, which is especially importantgiven the three-dimensional nature of the human balancing system. It isto be further understood that the number of stimulation elements andtheir specific location on the associated semicircular canals is alsosubject to variation so long as the actuation of these stimulationelements produces a rocking sensation in the patient.

In another embodiment of the present invention, the stimulation elementsare provided at ampullae 102, saccule 104, and/or utricle 106 ratherthan on, in or adjacent to the semicircular canals. The presentinvention contemplates using the stimulation techniques discussed abovewith respect to FIG. 8 to alternatively stimulate these structures tocreate a rocking sensation.

Because one object of this embodiment of the present invention is tosimulate rocking for the purpose of inducing sleep, a further variationof this embodiment of the present invention contemplates detecting whenthe patient has fallen asleep and automatically discontinuing therocking type stimulation. The present invention contemplates using anyone of the variety of known techniques to detect when the patient isasleep. The rocking type stimulation can then be decreased immediatelyonce sleep is detected or, preferably, gradually, so as not to arousethe patient from sleep. The present invention also contemplatesdiscontinuing the rocking type stimulation after a set duration, such asa predetermined period of time, following initiation of the stimulationtherapy. Such a stimulation would include a timer, for example, tomonitor the amount of time since the stimulation began or the amount oftime remaining until stimulation is to be discontinued. This embodimentof the present invention applies the rocking type stimulation to put thepatient to sleep, and discontinues the stimulation some time later,preferably once the patient has fallen asleep, much the same way a sleeptimer functions on a radio or television. Of course, the rocking typestimulation can continue even after the patient has fallen asleep. It isbelieved that stimulating a sleeping patient in this fashion helpspromote a more restful sleep.

The present invention also contemplates detecting the position of thepatient, such as whether the patient is in a recumbent or non-recumbentposition. This can be accomplished using, for example, a tilt switchlocated on the patient. In a preferred embodiment, the system detectswhen the patient is in a non-recumbent position, i.e., sitting up orstanding, and discontinues the vestibular stimulation when this isdetected.

Inducing a rocking sensation in the patient can also be donenon-invasively, using a vestibular stimulation system similar to thatshown in FIG. 2. In one embodiment, which is shown schematically in FIG.9, a first stimulating electrode 150 is located on the surface of thepatient proximate to a patient's left vestibular system 152, and asecond stimulating electrode 156 is disposed proximate to the patient'sright vestibular system 158. A control unit (not shown) appliesstimulation energy in the form of a varying current between first andsecond electrodes 150 and 156 to induce the rocking sensation. In FIG.9, lead wires are shown extending from electrodes 150 and 154. This isdone for ease of illustration to show the different types of varyingcurrent that can be applied between the electrodes. It is to beunderstood that these lead wires may be eliminated or reduced in scalefrom that shown, for example, of the vestibular stimulation system isconfigured to be worn on the patient's head.

The present invention contemplates that the varying current provided tothe vestibular system can have a single polarity or an alternatingpolarity. An alternating polarity current has a current that variesabove and below a zero reference line, i.e., varies between a positiveand a negative value. In FIG. 9, a triangular waveform 157, a sinusoidalvoltage waveform 158, and a square waveform 159 are all shown as havingan alternating polarity and are all examples of waveforms suitable foruse in this embodiment. It is to be understood, however, that any otherwaveform that induces a rocking sensation can be provided between thefirst and second stimulating electrodes. Triangle waveform 161,sinusoidal waveform 163, and square waveform 165 are waveforms having avarying current but having a single polarity, i.e., they do not dropbelow the zero baseline. As noted above, such single polarity, varyingcurrent waveforms are also suitable for use in this embodiment.

In a second embodiment, shown in FIG. 10, a first stimulating electrode160 and a second stimulating electrode 162 are provided proximate to thepatient's right vestibular system 152, and a third stimulating electrode164 and a fourth stimulating electrode 166 are provided proximate to thepatient's left vestibular system 156. A control unit (not shown) appliesstimulation energy in the form of a varying current having singlepolarity or an alternating polarity between first and second electrodes160 and 162 (pair A) and between third and fourth electrodes 164 and 166(pair B) to induce the rocking sensation.

The present invention contemplates stimulating the electrode pairs (pairA and pair B) together or in an alternating fashion. Stimulating theelectrode pairs in an alternating fashion means that a stimulatingwaveform 169 (single or alternating polarity) is applied to electrodepair A, while electrode pair B remain off, and vice versa. Thisstimulation technique is indicated by numeral 170 in FIG. 10.Stimulating the electrode pairs together means that both electrode pairsreceive a stimulating waveform, as indicated by numeral 172. In FIG. 10,the waveform applied to the electrode pairs is a varying currentwaveform having alternating polarities. As discussed below, the presentinvention also contemplates providing a single polarity varying currentto each electrode pair.

The waveform applied to each electrode pair can be identical to thewaveform applied to the other electrode pair. However, the presentinvention also contemplates that the waveforms applied to each electrodepair can be different, even though applied at the same time. Forexample, the waveform applied to one electrode pair can be phase shiftedrelative to the waveform applied to the other electrode pair. Thedifferent waveforms can also have different shapes, durations,magnitudes, polarities, or patterns.

FIG. 11 illustrates a few of the potentially infinite differenttechniques for stimulating the different electrode pairs. For example,numeral 180 identifies a pulse waveform having an alternating (positiveand negative) polarity applied to both electrode pairs (pair A and pairB). These waveforms can applied to each electrode pair so that thepolarities coincide, i.e., both electrode pairs receive a positive ornegative polarity, or are phase shifted, i.e., one electrode pairreceives a positive polarity while the other electrode pair receives anegative polarity and vice versa.

Alternatively, a single polarity pulse waveform can be applied in aalternating fashion, as indicated by 182, to the electrode pairs. Inthis situation, single polarity pulses are applied to one electrode pairwhile the other electrode pair receives no stimulation. Furthermore, thepresent invention contemplates providing pulses of a first polarity 184to a first electrode pair while pulses of a second polarity 186,preferably opposite the first polarity, are applied the other electrodepair, as indicated by numeral 188. It should be understood that theimportant feature of the present invention is to apply a waveform thatinduces a rocking sensation for the patient, not the specific shape orpolarity of the waveforms.

It should also be noted that the term “rocking” as used herein is notintended to be limited to a back and forth, i.e., posterior to anteriorand anterior to posterior motion, as is the conventional meaning of thisterm. On the contrary, the sensation of rocking also refers to thesensation of side to side, lateral or a swaying movement, as well as acombination of back and forth and sided to side motion, which can beconsidered a circular motion.

Counteracting Vertigo

A still further embodiment of the present invention contemplatesproviding stimulation to the appropriate portions of the vestibularsystem in an appropriately timed fashion so as to counteract dizzinessand/or vertigo, which is the sensation that the patient's surroundingsare whirling. Vertigo is the result of the vestibular system outputtingneurological signals according to a firing pattern that the brainrecognizes as a spinning sensation. Vertigo is not necessarily theresult of physically spinning the patient. However, dizziness may resultfrom such physical spinning.

The present invention contemplates counteracting vertigo and/ordizziness by stimulating the vestibular system in an offsetting fashionto, in effect, mask out or block the neural transmissions that the brainwould otherwise interpret as dizziness or a vertigo sensation. Forexample, suppose that the patient has the sensation that they arespinning to the left, which is the result of the vestibular systemoutputting neural signals in a first pattern. The present inventioncontemplates stimulating the vestibular system or portions thereof so asprevent this first pattern from being provided to the brain or to alterthe pattern being sent to the brain so that the brain no longer sensesthat the person is spinning. For example, if the firing frequency of theneurons slows down when the patient is spinning, thereby signaling thebrain that the person is spinning, the stimulation system of the presentinvention can be used to increase the neuron firing frequency, therebysignaling the brain that the person is not spinning.

This “blocking” function can be accomplished whether or not the personis actually spinning. For example, if the patient suffers from a balancedisorder, such as vertigo, the blocking function can be used to mask thesignals from the vestibular system that cause the brain to think thepatient is unbalanced even when they are not.

However, the present invention also contemplates providing stimulationto the vestibular system to counteract dizziness only if the patient isactually spinning. For example, the present invention contemplatesproviding an accelerometer as sensor 34 to detect acceleration ormovement of the patient's head or body. If acceleration is detected, thevestibular system is stimulated in a manner so as to counteract thedizzy sensation. This embodiment for the vestibular stimulation systemis particularly suited for applications where the user is likely toexperience dizziness but needs to continue performing functions that mayotherwise not be possible for someone experiencing vertigo. For example,a test pilot may experience vertigo if their plane enters a spin. Thepresent invention contemplates that the stimulation system detects thatthe pilot is spinning and initiates vestibular stimulation to counteractthe vertigo so that the pilot can attempt to regain control or eject,which are tasks that would otherwise be difficult it the pilot isexperiencing vertigo.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims.

What is claimed is:
 1. A vestibular stimulation system comprising: apower supply; a first, non-invasive electrode adapted to be disposed ona surface of a patient proximate to such a patient's left vestibularsystem; a second, non-invasive electrode adapted to be disposed on asurface of such a patient proximate to such a patient's right vestibularsystem; a control unit operatively coupled to the power supply, thefirst electrode, and the second electrode, wherein the control unitcontrols an application of the stimulation energy from the power supplyto at least a portion of such a patient's left or right vestibularsystem via the first or second electrodes, so as to induce a rockingsensation in such a patient by causing varying current waveform to beprovided between the first and the second electrodes.
 2. A systemaccording to claim 1, further comprising a position sensor to detect aposition of such a patient, and wherein the control unit controls theapplication of stimulation energy to the first and the second electrodesbased on an output of the position sensor.
 3. A system according toclaim 1, further comprising sleep detecting means for determining whensuch a patient is asleep, and wherein the control unit controls theapplication of stimulation energy to the first and the second electrodesbased on an output of the sleep determining means.
 4. A system accordingto claim 1, wherein the varying current waveform applied between thefirst and the second electrodes has a single polarity or an alternatingpolarity.
 5. A vestibular stimulation system comprising: a power supply;a first pair of non-invasive electrodes adapted to be disposed on asurface of a patient proximate to a vestibular system on a first side ofsuch a patient; a control unit operatively coupled to the power supplyand the first pair of electrodes, wherein the control unit controls anapplication of the stimulation energy from the power supply to at leasta portion of such a patient's vestibular system via the first pair ofelectrodes so as to induce a rocking sensation in such a patient bycausing a first waveform having a varying current to be provided betweenthe electrodes in the first pair of electrodes.
 6. A system according toclaim 5, wherein the first waveform applied between the electrodes inthe first pair of electrodes has a single polarity or an alternatingpolarity.
 7. A system according to claim 5, further comprising aposition sensor to detect a position of such a patient, and wherein thecontrol unit controls the application of stimulation energy to the firstpair of electrodes based on an output of the position sensor.
 8. Asystem according to claim 5, further comprising sleep detecting meansfor determining when the patient is asleep, and wherein the control unitcontrols the application of stimulation energy to the first pair ofelectrodes based on an output of the sleep determining means.
 9. Asystem according to claim 5, further comprising a second pair ofnon-invasive electrodes adapted to be disposed on a surface of a patientproximate to a vestibular system on second side of such a patient, andwherein the control unit controls an application of the stimulationenergy from the power supply to at least a portion of such a patient'svestibular system via the second pair of electrodes so as to induce arocking sensation in such a patient by causing a second waveform havinga varying current to be provided between the electrodes in the secondpair of electrodes.
 10. A system according to claim 9, wherein the firstwaveform applied between the electrodes in the first pair of electrodesand the second waveform applied between the electrode in the second pairof electrodes has a single polarity or an alternating polarity.
 11. Asystem according to claim 9, wherein the first waveform and the secondwaveform are identical so that the first and the second pair ofelectrode receive identical stimulation energy.
 12. A system accordingto claim 9, wherein the first waveform and the second waveform aredifferent from one another.
 13. A system according to claim 9, whereinthe control unit causes the system to operate in a first stimulatingpattern in which the first waveform is provided between the electrodesin the first pair of electrodes and no stimulation energy is provided tothe second pair of electrodes and in a second stimulating pattern inwhich the second waveform is provided between the electrodes in thesecond pair of electrodes and no stimulation energy is provided to thefirst pair of electrodes, and wherein the control unit periodicallyswitches between the first stimulating state and the second stimulatingstate.
 14. A vestibular stimulation method comprising: providing afirst, non-invasive electrode disposed on a surface of a patientproximate to such a patient's left vestibular system; providing asecond, non-invasive electrode disposed on a surface of such a patientproximate to such a patient's right vestibular system; applyingstimulation energy in the form of varying current waveform providedbetween the first and the second electrodes so as to induce a rockingsensation in such a patient.
 15. A method according to claim 14, whereinthe varying current waveform has a single polarity or an alternatingpolarity.
 16. A method according to claim 14, further comprising:detecting a position of such a patient; and controlling the applicationof stimulation energy to the first and the second electrodes based onthe position of such a patient.
 17. A method according to claim 14,further comprising: determining when such a patient is asleep; andcontrolling the application of stimulation energy to the first and thesecond electrodes based on an output of the sleep determining means. 18.A vestibular stimulation method comprising: providing a first pair ofnon-invasive electrodes on a surface of a patient proximate to avestibular system on a first side of such a patient; applyingstimulation energy to at least a portion of such a patient's vestibularsystem via the first pair of electrodes, so as to induce a rockingsensation in such a patient, by causing a first waveform having avarying current to be provided between the electrodes in the first pairof electrodes.
 19. A method according to claim 18, wherein the firstwaveform applied between the electrodes in the first pair of electrodeshas a single polarity or an alternating polarity.
 20. A method accordingto claim 18, further comprising: detecting a position of such a patient;and controlling the application of stimulation energy to the first pairof electrodes based on the position of the patient.
 21. A methodaccording to claim 18, further comprising: determining when such apatient is asleep; and controlling the application of stimulation energyto the first and the second electrodes based on an output of the sleepdetermining means.
 22. A method according to claim 18, furthercomprising: providing a second pair of non-invasive electrodes disposedon a surface of a patient proximate to a vestibular system on secondside of such a patient; and applying stimulation energy to at least aportion of such a patient's vestibular system via the second pair ofelectrodes, so as to induce a rocking sensation in such a patient, bycausing a second waveform having a varying current to be providedbetween the electrodes in the second pair of electrodes.
 23. A methodaccording to claim 22, wherein the first waveform applied between theelectrodes in the first pair of electrodes has a single polarity or analternating polarity and wherein the second waveform applied between theelectrodes in the second pair of electrodes has a single polarity or analternating polarity.
 24. A method according to claim 22, wherein thefirst waveform and the second waveform are identical so that the firstand the second pair of electrode receive identical stimulation energy.25. A method according to claim 22, wherein the first waveform and thesecond waveform are different from one another.
 26. A method accordingto claim 22, applying stimulation energy to the first and the secondpair of electrodes includes: providing stimulating energy in a firststimulating pattern in which the waveform is provided between theelectrodes in the first pair of electrodes and no stimulation energy isprovided to the second pair of electrodes; providing stimulating energyin a second stimulating pattern in which the second waveform is providedbetween the electrodes in the second pair of electrodes and nostimulation energy is provided to the first pair of electrodes; andperiodically switching between providing the stimulating energy in thefirst stimulating pattern and in the second stimulating pattern.